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Discussion Starter · #1 · (Edited)
My 1999 Outback, (2.5 DOHC, manual trans, correct mileage unknown but likely 200k +, good coil pack, rebuilt injectors, new spark plugs) has been giving me cyl 3 and sometimes cyl 4 misfire CEL codes for a while under very specific conditions - 3300 to 3500 rpm in 5th gear (freeway driving) when I let off the throttle. (Can't feel any misfire at all.) After clearing the codes, it usually takes several instances of these conditions before the code(s) reappear. Once the misfire code is set, I also get the flashing CEL frequently under the specific conditions. I never get the misfire codes when driving around town, even for several weeks, but I rarely hit 3300+ rpm around town. It seems to me that these circumstances suggest that the EGR system is the source of the codes, particularly since the EGR valve dumps into the cyl 3 intake runner. I'm thinking that an excess of exhaust gas is being dumped overwhelming the fuel air mixture ratio. (Do the injectors remain closed under these conditions? no fuel?) I have tested the EGR valve itself with a vacuum pump - seems to work as it should. And the EGR solenoid would seem to be working since the codes are set only above 3300 rpm. So, I have just replaced the BPT after inconclusive attempts to test it. Haven't had a chance to do some highway running (3300+ rpm, 5th gear, trailing throttle) to see if that is/was the problem. I have three questions: 1) If the BPT was defective, would the EGR valve still open? 2) Is it possible that the EGR valve spring is weak so that the EGR valve opens too much, too long? 3) Am I correct in thinking that an excess of exhaust gas dumped by the EGR would cause the misfire code?


Update: New BPT did not fix. Still posting cyl 3 and 4 misfire at stated conditions.

I also just found that I'm consuming some oil when running at 70-75 mph for long periods. Consumed about 1 quart on each of two recent highway trips of 1200 miles but don't seem to consume oil after many weeks of around town driving rarely getting up to 3000 rpm. Can a PCV get weaker over time so that it is venting the crankcase too much during higher speed running and causing higher oil consumption?


Thanks for any help.
 
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